Chaperone-like N-Methyl Peptide Inhibitors of Polyglutamine Aggregation

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• 作者：Jennifer D. Lanning ; Andrew J. Hawk ; JohnMark Derryberry ; Stephen C. Meredith
• 刊名：Biochemistry
• 出版年：2010
• 出版时间：August 24, 2010
• 年：2010
• 卷：49
• 期：33
• 页码：7108-7118
• 全文大小：1152K
• 年卷期：v.49,no.33(August 24, 2010)
• ISSN：1520-4995

文摘

Polyglutamine expansion in the exon 1 domain of huntingtin leads to aggregation into β-sheet-rich insoluble aggregates associated with Huntington’s disease. We assessed eight polyglutamine peptides with different permutations of N-methylation of backbone and side chain amides as potential inhibitors of polyglutamine aggregation. Surprisingly, the most effective inhibitor, 5QMe₂ [Anth-K-Q-Q(Me₂)-Q-Q(Me₂)-Q-CONH₂, where Anth is N-methylanthranilic acid and Q(Me₂) is side chain N-methyl Q], has only side chain methylations at alternate residues, highlighting the importance of side chain interactions in polyglutamine fibrillogenesis. Above a 1:1 stoichiometric ratio, 5QMe₂ can completely prevent fibrillation of a synthetic aggregating peptide, YAQ₁₂A; it also shows significant inhibition at substoichiometric ratios. Surface plasmon resonance (SPR) measurements show a moderate K_d with very fast k_on and k_off values. Sedimentation equilibrium analytical ultracentrifugation indicates that 5QMe₂ is predominantly or entirely monomeric at concentrations of ≤1 mM and that it forms a 1:1 stoichiometric complex with a fibril-forming target, YAQ₁₂A. 5QMe₂ inhibits not only nucleation of YAQ₁₂A but also fibril extension, as shown by the fact that it also inhibits seeded fibril growth where the nucleation steps are bypassed. 5QMe₂ acts on its targets only when they are in the PPII-like conformation, but not after they undergo a transition to β-sheets. Thus, 5QMe₂ does not disassemble preformed YAQ₁₂A; this contrasts with our previously described, backbone N-methylated inhibitors of β-amyloid aggregation [Gordon, D. J., et al. (2001) Biochemistry 40, 8237−8245; Gordon, D. J., et al. (2002) J. Pept. Res. 60, 37−55]. The mode of action of 5QMe₂ is reminiscent of that of chaperones, because it binds and releases its targets very rapidly and maintains them in a nonaggregation-prone, monomeric state, in this case, the polyproline II (PPII)-like conformation, as shown by circular dichroism spectroscopy.